Wetting Kinetics of a Thin Film Evaporating in Air

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Abstract

The conservation equation and the equations of motion are solved for a case where a thin liquid film moves out of a slot onto a horizontal surface. The liquid is allowed to evaporate into air. The evaporation process is taken to be isothermal. Lubrication theory approximation is used where only the tangential velocity and its dependence only in the normal direction are considered. The dynamics of thin films includes the use of disjoining pressure for a pure liquid and where there is a dissolved polymer. The results show that evaporation is quicker than film thinning such that a spreading regime dominated by the effects of disjoining pressure is never achieved. However, unlike the cases of pinning studied so far, there is no singularity in the evaporative flux near the contact line because of the use of disjoining pressure on evaporation. It is also observed that a balance between the rate of viscous dissipation and surface work is able to quantify the steady state contact angle. Consequently, a more macroscopic (and quantitative) description of contact line can be found that avoids the singularities discussed earlier and also the detailed calculations shown here. However, the detailed calculations are necessary to make the above point.